Method of forming

ABSTRACT

This invention relates to a method of forming a sheet metal article such as an electrical contact wherein the direction of bending of the article is the same as the direction of shear, whereby the stress areas of said article are maintained at the inner portion of the bends in the article, thereby minimizing the chance of subsequent fracture.

United States Patent Inventor Linn Stephen Lightner Camp Hill, Pa. Appl. No. 495,892 Filed Oct. 14, 1965 Patented Apr. 13, 1971 Assignee AMP incorporated Harrisburg, Pa.

METHOD OF FORMING 3 Claims, 5 Drawing Figs.

11.8. CI 72/339, 72/379, 72/330 Int, Cl 821d 31/02, B2lc 37/02, B21d 28/00 Field of Search 72/339,

330, 335, (EC); 29/62830, (lnquired); 1 13/1 19 [5 6] References Cited UNITED STATES PATENTS 503,035 8/1893 Budlong 72/330 2,004,555 6/1935 Kleinmann 72/335 2,643,446 6/1953 Matthysse et a1. 1 13/1 19 Primary Examiner-Richard J Herbst Assistant Examiner-R. M. Rogers AttorneysCurtis, Morris and Safford, Marshall M.

Holcombe, William Hintze, William J. Keating, Frederick W. Raring, John R. Hopkins, Adrian J. La Rue and Jay L. Seitchik METHOD OF FORMING This invention relates to the art of forming and more particularly to a new and novel method of forming an article from a thin strip of sheet metal material.

There are many fields where articles are employed which have been formed or stamped from thin sheet metal. One such field is the electronic industry where numerous electrical pans are stamped in huge volume. The sheet metal strip from which these parts are formed is usually quite thin, in the order of a few mils, and the parts themselves must often undergo severe bending. Such severe bending generates severe stresses in the finished product and it has been a common problem in the industry to devise a method whereby the subsequent fracture of these electrical parts at the areas of severe stress could be eliminated.

The method commonly employed in the industry today of forming the sheet metal partsis merely to blank such parts from a sheet metal strip in a single stroke of the blanking dies and subsequently forming the parts into their final shape by a series of banding steps. Such a method enables high production of parts but does not avoid the problem of fracture of some of these parts during their subsequent use. The unique method of this invention maintains the volume of production capable by the present known methods while eliminating completely the possibility of fractures in the finished parts.

It is therefore the principal object of the present invention to provide a method of stamping parts from a sheet metal strip while obviating the possibility of subsequent fracture of the parts.

Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there is shown and described an illustrative embodiment of the invention; it is to be understood, however, that this embodiment is not intended to be exhaustive nor limiting of the invention but is given for purpose of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.

In the drawings, in which like reference numerals refer to like parts:

FIG. I is a perspective view of a sheet metal part made in accordance with the improved method of the present invention;

FIG. 2 is a perspective view showing the progression of the part of FIG. I during various stages of its manufacture;

FIG. 3 is a cross-sectional view taken along the line 33 of FIG. 1; and

FIGS. 4 and 5 are cross-sectional views showing bending stresses in a formed sheet metal part.

In FIG. I there is shown a formed article 2, the article chosen for purposes of illustration being an electrical contact. The article consists of a barrel-shaped portion 4, an intermediate connecting strip 6, and a boxlike receptacle portion 8. The barrel 4 would ultimately be crimped around a wire conductor in a conventional manner and the receptacle 8 could suitable receive a male contact tab. The important feature of the article 2 as far as the unique method of the present invention is concerned resides in the fact that the barrel 4 is bent in the opposite direction from the receptacle portion 8. It is this two directional bending of the sheet metal article which gives rise to the most serious problems of article fracture.

Turning now to FIG. 2 there is illustrated the various manufacturing stages necessary to produce the article shown in FIG. I. The thin metallic sheet is passed through a first blanking station A whereat the material to form the receptacle 8 and connecting strip 6 is blanked from the sheet 2 by an upwardly directed blanking die. At this point the receptacle 8 and connecting strip 6, in their fiat form, are severed from sheet I0; however, they remain secured to sheet 10 by the end of connecting strip 6. The sheet then passes through a second blanking and forming station B whereat the barrel portion 4 is blanked from sheet It) and the receptacle portion 8 is partially formed. The barrel portion 4 is severed from the strip by a downwardly directed blanking die.

At this point it is necessary for a complete understanding of the present invention to analyze the surface characteristics of the article thus formed. The characteristics of the article 2 after the blanking operations have been performed can be best seen with reference to the cross-sectional view of FIG. 3. As stated above, the receptacle 8 and connecting strip 6 have been severed from the metal sheet 10 by an upwardly directed blanking die, the direction being shown by the arrow 12. The barrel portion 4 has been severed from the sheet 10 by a downwardly directed blanking die indicated by the arrow 14. The movement of the blanking dies through the sheet 10 produces localized stresses which are graphically shown in FIG. 3. When a blanking die passes through a sheet of metal there is produced a clean line of severance for the majority of the thickness of the metal. However, as the die approaches the completion of its cut, the material adjacent the trailing edge of the sheet becomes quite'brittle due to high stresses developed in the metal with the result that the line of severance becomes quite ragged as indicated at 16 and 18. The trailing edge of a sheet of metal will contain a series of minute ridges, shown greatly exaggerated at 20 and 22, in contrast with the smooth edge found at the leading edge of the sheet. It has been found that these small ridges are responsible for a great number of l the fractures of the formed sheet metal parts.

Returning again to FIG. 2, the blanked article2 is passed through a forming station C wherein the receptacle portion 8 is bent upwardly into its final configuration and the barrel portion 4 is bent downwardly into its final configuration. It can be seen at this point that the metal article has been bent in the same direction as it has been sheared, this factor representing the essence of the present invention. Finally, at station D the remainder of strip 6 is severed to free the article 2 from sheet 10.

In FIG. 4 there is shown a cross section of a sheet metal article which has been bent by the present known methods. The article has been blanked downwardly to produce the ridges 24 on the lower surface thereof and subsequently the article has been bent upwardly so that these ridges 24 occupy the outer surface of the bent area. By bending the sheet metal as shown in FIG. 4 the surfacefibers along the radially inward surface of the bend are placed in compression while the surface fibers on the radially outward side of the bend are placed in tension. The tensile forces along the exterior surface attempt to separate the fibers from each other. Due to the ridges on this surface, there are a great number of weakened areas wherein a number of cracks such as 26 may develop.

In contrast to this there is shown in FIG. 5 a cross section of i a metal article which has been bent in conformance with the teaching of the present invention. It can be seen that by bending the article in the same direction as which it has been blanked or sheared the ridges 28 and high-stress area of the metal are adjacent the inner surface of the bend where the fibers are subjected to compressive forces. Under compression there is no tendency for the fibers to separate and therefore the ridges have no detrimental effect. On the outside surface of the bend where the fibers are subjected to the tensile forces, there is a sharp clean surface where no localized weakened portions are present.

It can therefore be seen that the objects of the present invention have been attained by producing an article wherein the various portion of the article are blanked or sheared in the same direction in which they are to be subsequently bent.

Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective against the prior art.

lclaim:

l. A method of forming an electrical contact wherein said contact comprises a receptacle portion and a securing portion for connecting the contact to an electrically conductive element, said method comprising the steps of severing said receptacle portion from a metallic sheet in a first direction, severing said securing portion from said metallic sheet in a second opposite direction, bending said receptacle portion in said first direction, and bending said securing portion in said second direction whereby the irregular surfaces produced in said contact by the severing steps are disposed along the radially inward faces of the bends in said receptacle and securing portions.

2. A method of forming a sheet metal article comprising the steps of shearing a first section of sheet metal in a first direction, shearing a second section of said sheet metal in a second direction, said first and second directions being approximately apart, bending said first section in said first direction to form a first portion of said article, and bending said second section in said second direction to form a second portion of said article.

3. A method of forming a sheet metal article comprising the steps of shearing a first section of sheet metal in an upward direction, shearing a second section of said sheet metal in a downward direction, said first and second sections being adjacent to each other, bending said first section upwardly to form a first portion of said article whereby the upper surface of said first section is subjected to compressive forces and the lower surface of said first section is subjected to tensile forces, and bending said second section downwardly to form a second portion of said article whereby the lower surface of said second section is subjected to compressive forces and the upper surface of said second section is subjected to tensile forces. 

1. A method of forming an electrical contact wherein said contact comprises a receptacle portion and a securing portion for connecting the contact to an electrically conductive element, said method comprising the steps of severing said receptacle portion from a metallic sheet in a first direction, severing said securing portion from said metallic sheet in a second opposite direction, bending said receptacle portion in said first direction, and bending said securing portion in said second direction whereby the irregular surfaces produced in said contact by the severing steps are disposed along the radially inward faces of the bends in said receptacle and securing portions.
 2. A method of forming a sheet metal article comprising the steps of shearing a first section of sheet metal in a first direction, shearing a second section of said sheet metal in a second direction, said first and second directions being approximately 180* apart, bending said first section in said first direction to form a first portion of said article, and bending said second section in said second direction to form a second portion of said article.
 3. A method of forming a sheet metal article comprising the steps of shearing a first section of sheet metal in an upward direction, shearing a second section of said sheet metal in a downward direction, said first and second sections being adjacent to each other, bending said first section upwardly to form a first portion of said article whereby the upper surface of said first section is subjected to compressive forces and the lower surface of said first section is subjected to tensile forces, and bending said second section downwardly to form a second portion of said article whereby the lower surface of said second section is subjected to compressive forces and the upper surface of said second section is subjected to tensile forces. 